Compact drive apparatus

ABSTRACT

A hydrostatic transaxle with a bypass mechanism is disclosed, the transaxle having a center section engaged to a housing, an axial piston pump disposed on the center section and driven by an input shaft, and an axial piston motor disposed on the center section having a cylinder block engaged to a motor shaft. The pump is controlled by a swash plate having a pair of openings through which the input shaft and a bypass actuation rod pass. The bypass actuation rod has a cam formed on a first end that engages a block lift member. When the bypass actuation rod is rotated, the cam causes the block lift member to engage and lift the cylinder block of the axial piston motor off of the center section. A brake mechanism using brake puck disposed in a pocket formed in the center section is also disclosed.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims the benefit of Provisional Application Ser. No. 61/708,775, filed Oct. 2, 2012, which is incorporated herein by reference in its entirety.

BACKGROUND OF THE INVENTION

This application relates to a hydrostatic drive apparatus generally, and in particular to a hydrostatic transaxle with a bypass mechanism and a brake mechanism. The transaxle is intended for use in driving a vehicle or other powered machine or apparatus.

SUMMARY OF THE INVENTION

An improved hydrostatic transaxle with a bypass mechanism and a brake mechanism is disclosed herein, as described in more detail below. The transaxle can be mounted on a vehicle or other powered machine or apparatus.

A better understanding of the objects, advantages, features, properties and relationships of the invention will be obtained from the following detailed description and accompanying drawings which set forth illustrative embodiments that are indicative of the various ways in which the principles of the invention may be employed.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of a first embodiment of a transaxle in accordance with the teachings herein.

FIG. 2 is a perspective view of a second embodiment of a transaxle in accordance with the teachings herein.

FIG. 3 is a perspective view of a portion of the transaxle of FIG. 2 with certain components removed for clarity.

FIG. 4 is a plan view of the portion of the transaxle shown in FIG. 3.

FIG. 5 is a cross-sectional view along line 5-5 in FIG. 4.

FIG. 6 is a perspective view of the portion of the transaxle shown in FIG. 3, rotated 180° about the axis of input shaft 229, with the side housing removed for clarity.

FIG. 7 is a perspective view of the portion of the transaxle shown in FIG. 3, rotated 90° about the axis of input shaft 229, with certain additional components removed for clarity.

FIG. 8 is a perspective view of the portion of the transaxle shown in FIG. 7, rotated 180° about the axis of bypass rod 262, with certain additional components removed for clarity.

DETAILED DESCRIPTION OF THE DRAWINGS

The description that follows describes, illustrates and exemplifies one or more embodiments of the invention in accordance with its principles. This description is not provided to limit the invention to the embodiment(s) described herein, but rather to explain and teach the principles of the invention in order to enable one of ordinary skill in the art to understand these principles and, with that understanding, be able to apply them to practice not only the embodiment(s) described herein, but also any other embodiment that may come to mind in accordance with these principles. The scope of the invention is intended to cover all such embodiments that may fall within the scope of the appended claims, either literally or under the doctrine of equivalents.

It should be noted that in the description and drawings, like or substantially similar elements may be labeled with the same reference numerals. However, sometimes these elements may be labeled with differing numbers or serial numbers in cases where such labeling facilitates a more clear description. Additionally, the drawings set forth herein are not necessarily drawn to scale, and in some instances proportions may have been exaggerated to more clearly depict certain features. As stated above, this specification is intended to be taken as a whole and interpreted in accordance with the principles as taught herein and understood by one of ordinary skill in the art. It will be further understood that for clarity in certain cross-sectional views, certain elements are not shown in cross-section, as doing so would not assist in the understanding of the disclosure herein. For example, in FIG. 5, the various shafts depicted are not cross-sectioned merely for clarity in the drawing.

FIG. 1 shows a first embodiment of a hydrostatic transaxle 120. Side housing 123 is secured to main housing 122 with fasteners 124. Axle 182 b extends from side housing 123 and axle 182 a extends from main housing 122. Pump input shaft 129 also extends from main housing 122 and may have a pulley (not shown) fixed thereon capable of receiving a drive belt (not shown). Bypass arm 161 is fixed to a portion of bypass rod 162 extending from main housing 122 and control arm 136 is fixed to trunnion 135 a extending from main housing 122.

FIGS. 2-8 show a second embodiment of a hydrostatic transaxle 220, which can be identical in most respects to hydrostatic transaxle 120, particularly with respect to its internal components. Hydrostatic transaxle 220, however, has an axle horn 225 disposed about axle 282 b that is separate from, and fastened to, side housing 223. Transaxle 220 further includes a detached pillow block 226 disposed about axle 282 a. Axle horn 225 and pillow block 226 allow mounting of hydrostatic transaxle 220 to a frame, e.g. of a vehicle (not shown).

FIG. 3 identifies transmission 221, reduction gear train 280, and differential 281. Transmission 221 includes axial piston pump 230 which hydraulically communicates with axial piston motor 240 through the porting (not shown) of center section 250. Center section 250 is secured in main housing 222 by fasteners 251.

FIG. 5 shows many of the details of transmission 221. Pump input shaft 229 extends through opening 235 c in swash plate 235 to the exterior of main housing 222. Pump input shaft 229 is rotatably supported in input shaft bore 250 i of center section 250 and is further supported by a bearing (not shown) in input shaft opening 222 c. Pump cylinder block 231 is engaged to pump input shaft 229 which rotates about axis of rotation 229Ax. Pump cylinder block 231 has pump pistons 231 a axially disposed therein and runs on pump running surface 250 a of center section 250. Swash plate 235 controls the output of axial piston pump 230 in a known manner as a result of the rotation of swash plate 235 about axis of rotation 235Ax. Such rotation changes the angle of pump thrust bearing 232, which is seated in swash plate 235, relative to the axial alignment of pump pistons 231 a to generate hydraulic fluid flow. Swash plate 235 has a trunnion 235 a which is rotatably journaled in trunnion support opening 222 a, and a trunnion 235 d which is rotatably supported in trunnion support pocket 223 b. Thus, swash plate 235 is rotatably supported by both the main housing 222 and the side housing 223.

Motor cylinder block 241 has pistons 241 a axially disposed therein and runs on motor running surface 250 b, which generally lies perpendicular to pump running surface 250 a. The flow of hydraulic fluid from axial piston pump 230 into pistons 241 a causes the pistons 241 a to bear against motor thrust bearing 242. Because motor thrust bearing 242 is seated at a fixed angle in pocket 222 b of main housing 222, motor cylinder block 241 is urged to rotate. Motor cylinder block 241 is slidingly engaged to motor output shaft 245 at a first end and causes it to rotate about axis of rotation 245Ax. Reduction gear train 280 is engaged to motor output shaft 245 proximate to its second end, being driven thereby. Motor output shaft 245 is rotatably journaled in center section 250 via a pair of cylindrical bores 250 g, 250 j separated by an intervening channel 250 k, and further supported at its second end by a motor shaft support pocket 223 c formed in side housing 223. Channel 250 k lies generally perpendicular to, and is intersected by, input shaft bore 250 i.

A hydraulic circuit exists between axial piston pump 230 and axial piston motor 240 that is normally closed during operation of transaxle 220 with the exception of make-up hydraulic fluid from sump 255, which can enter the circuit through one of check plug ports 250 c shown in FIG. 8. Check plug ports 250 c communicate with the internal porting (not shown) of center section 250 and accept check plugs (not shown) that will allow make-up hydraulic fluid to be drawn into the check plug port 250 c that communicates with the low pressure or suction side of the hydraulic circuit, compensating for fluid losses during operation. In order to minimize the size of center section 25, as can be seen in FIG. 8, the two check plug ports 250 c and the bore 250 j form a triangular shape on one end of center section 250.

A block-lift bypass mechanism 260 allows axles 282 a and 282 b to freely rotate when hydrostatic transaxle 220 is not under power. This allows an operator of a vehicle having hydrostatic transaxle 220 to freely move the vehicle without powering it up, e.g. when servicing the vehicle. Bypass actuation rod 262 extends through swash plate opening 235 b and passes through main housing 222 to its exterior, the bypass actuation rod 262 being oriented generally parallel to pump input shaft 229. Similar to opening 235 c, swash plate opening 235 b is sized, shaped, and located to allow rotation of swash plate 235 without interference with the function of pump thrust bearing 232. Bypass actuation rod 262 is rotatably supported in bypass rod support bore 250 d as shown in FIG. 8. Block lift member 263 is movably disposed in cavity 250 h of center section 250 and bears against bypass rod cam surface 262 a. When bypass actuation rod 262 is rotated about axis of rotation 262Ax, cam surface 262 a causes block lift member 263 to contact and lift motor cylinder block 241 from the motor running surface 250 b. This lift breaks hydraulic fluid communication between motor pistons 241 a and the fluid ports 250 f in motor running surface 250 b; and more generically, it breaks the fluid communication between axial piston pump 230 and axial piston motor 240. Thus, motor output shaft 245, reduction gear train 280, and axles 282 a, 282 b are free to rotate without hydraulic resistance. The location of bypass actuation rod 262 extending through an opening in swash plate 235 permits a smaller, more compact unit.

FIGS. 4-6 best illustrate brake mechanism 270. Pin 274 is transversely fixed in brake shaft 272 and rides on a cam projection 223 a formed on side housing 223. When brake shaft 272 is rotated either clockwise or counterclockwise, via corresponding rotation of brake arm 271 from an initial position to a rotated position, the interaction of pin 274 and cam projection 223 a moves brake shaft 272 axially into contact with brake rotor 276. Brake rotor 276 is disposed about and slidingly engaged to motor output shaft 245, proximate to its second end. As brake shaft 272 is rotated further, additional axial movement forces brake rotor 276 into frictional engagement with brake puck 275, to brake motor output shaft 245. As can be seen most clearly in FIG. 8, brake puck 275 is disposed in a brake puck pocket 250 e formed in center section 250, and brake puck pocket 250 e is preferably adjacent to one of the check plug ports 250 c to minimize the size of center section 250. Spring 273 is disposed about brake shaft 272 between brake arm 271 and side housing 223, bearing against each to bias brake mechanism 270 to a disengaged state. The bidirectional nature of brake mechanism 270 permits an external brake linkage (not shown) to actuate brake mechanism 270 in either rotational direction.

Referring again to FIG. 5, it can be seen that axes of rotation 229Ax, 235Ax, 245Ax, and 262Ax lie within a common plane. This also allows for a more compact transaxle suitable for application to smaller utility vehicles.

While one or more specific embodiments of the invention have been described in detail, it will be appreciated by those skilled in the art that various modifications and alternatives to those details could be developed in light of the overall teachings of the disclosure. Accordingly, the particular arrangements disclosed are meant to be illustrative only and not limiting as to the scope of the invention which is to be given the full breadth of any appended claims and any equivalent thereof. 

What is claimed is:
 1. A drive apparatus disposed in a housing, the drive apparatus comprising: a pump running surface and a motor running surface disposed in the housing; an axial piston pump disposed on the pump running surface and controlled by a swash plate having a pair of openings formed therein; an axial piston motor comprising a motor cylinder block disposed on the motor running surface and in fluid communication with the axial piston pump; a motor shaft rotationally supported in the housing and drivingly engaged to the motor cylinder block; an input shaft drivingly engaged to the axial piston pump and rotationally supported in the housing, wherein the input shaft extends through one of the pair of openings in the swash plate and one end of the input shaft extends out of the housing; a block lift member moveably disposed adjacent the motor cylinder block; and a bypass actuation rod having a first end engaged to the block lift member, wherein the bypass actuation rod extends through the other one of the pair of openings in the swash plate and out of the housing; wherein, rotation of the bypass actuation rod causes the block lift member to contact and lift the motor cylinder block off the motor running surface to break the fluid communication between the motor cylinder block and the axial piston pump.
 2. The drive apparatus of claim 1, wherein the first end of the bypass actuation rod is formed as a cam.
 3. The drive apparatus of claim 1, further comprising: a center section on which the pump running surface and the motor running surface are formed, the center section further comprising a brake puck pocket; a brake rotor disposed about and slidingly engaged to the motor shaft; a brake shaft extending through the housing and having a first end disposed proximate to one side of the brake rotor; a pin extending transversely through the brake shaft; a brake puck disposed in the brake puck pocket, opposite the brake shaft; a cam projection formed on an internal surface of the housing and engaged to the pin, wherein rotation of the brake shaft causes the pin to follow the cam projection and move the brake shaft into contact with the brake rotor, bringing the brake rotor into frictional engagement with the brake puck.
 4. The drive apparatus of claim 3, further comprising a brake arm fixed to a second end of the brake shaft external to the housing.
 5. The drive apparatus of claim 4, further comprising a spring disposed about the brake shaft between the brake arm and the housing, wherein the spring biases the brake shaft to a position where the brake rotor is not in frictional engagement with the brake puck.
 6. The drive apparatus of claim 3, wherein the cam projection is formed to permit the brake shaft to be rotated clockwise or counterclockwise to bring the brake rotor into frictional engagement with the brake puck.
 7. The drive apparatus of claim 1, further comprising a reduction gear set engaged to the motor shaft to be driven thereby and a pair of axles engaged to the reduction gear set through a differential.
 8. The drive apparatus of claim 1, wherein the housing comprises a main housing and a side housing, and the swash plate is rotationally supported by both the main housing and the side housing and the motor shaft is rotationally supported by the side housing.
 9. The drive apparatus of claim 1, wherein the bypass actuation rod is oriented generally parallel to the input shaft.
 10. The drive apparatus of claim 1, wherein the respective axes of rotation for the input shaft, bypass actuation rod, swash plate, and motor shaft lie in a common plane.
 11. The drive apparatus of claim 1, further comprising a center section mounted in the housing, wherein the pump running surface and the motor running surface are both formed on the center section, and at least a portion of the block lift member is disposed inside the center section, and the bypass actuation rod is rotationally supported by the center section.
 12. A drive apparatus, comprising: a center section disposed in a housing and having a pump running surface and a motor running surface formed thereon; an axial piston pump disposed on the pump running surface and driven by an input shaft having a first axis of rotation, wherein one end of the input shaft extends out of the housing; a swash plate disposed in the housing and engaged to the axial piston pump to control the output thereof, the swash plate being engaged to and rotated by a trunnion that includes a portion that extends out of the housing, the trunnion having a second axis of rotation that is perpendicular to the first axis of rotation; an axial piston motor comprising a motor cylinder block disposed on the motor running surface, wherein the axial piston motor is in fluid communication with the axial piston pump; a motor shaft rotationally supported in the housing and engaged to the motor cylinder block to be driven thereby, the motor shaft having a third axis of rotation that is parallel to the second axis of rotation; a block lift member disposed adjacent the motor cylinder block and a bypass actuation rod having a first end engaged to the block lift member, wherein the bypass actuation rod has a fourth axis of rotation that is parallel to the first axis of rotation and rotation of the bypass actuation rod causes the block lift member to contact and lift the motor cylinder block off the motor running surface to break the fluid communication between the motor cylinder block and the axial piston pump, and the first, second, third and fourth axes of rotation lie in a common plane.
 13. The drive apparatus of claim 12, wherein the bypass actuation rod extends through an opening formed in the swash plate.
 14. The drive apparatus of claim 12, further comprising: a brake rotor disposed about and slidingly engaged to the motor shaft; a brake shaft extending through the housing and having a first end disposed proximate to one side of the brake rotor, the brake shaft having a fifth axis of rotation that is parallel to the third axis of rotation; a pin extending transversely through the brake shaft; a brake puck disposed in a brake puck pocket formed in the center section, and opposite the brake shaft; and a cam projection formed on an internal surface of the housing and engaged to the pin, wherein rotation of the brake shaft causes the pin to follow the cam projection and move the brake shaft into contact with the brake rotor, bringing the brake rotor into frictional engagement with the brake puck.
 15. The drive apparatus of claim 14, further comprising a brake arm fixed to a second end of the brake shaft external to the housing, and a spring disposed about the brake shaft between the brake arm and the housing, wherein the spring biases the brake shaft to a position where the brake rotor is not in frictional engagement with the brake puck.
 16. A hydraulic drive apparatus, comprising: a center section disposed in a housing and having a pump running surface and a motor running surface formed thereon; a hydraulic pump disposed on the pump running surface and a hydraulic motor disposed on the motor running surface and in fluid communication with the hydraulic pump; a motor shaft engaged to the hydraulic motor to be driven thereby; and a brake mechanism for providing a braking force to the motor shaft, comprising: a brake rotor disposed about and slidingly engaged to the motor shaft; a brake shaft extending through the housing and having a first end disposed proximate to one side of the brake rotor; and a brake puck disposed in a brake puck pocket formed in the center section, proximate to a second side of the brake rotor.
 17. The hydraulic drive apparatus of claim 16, further comprising a cam formed on an internal surface of the housing to move the brake shaft into contact with the brake rotor, bringing the brake rotor into frictional engagement with the brake puck, when the brake shaft is rotated.
 18. The hydraulic drive apparatus of claim 16, wherein the brake puck is located opposite the brake shaft, and the braking force is transmitted along an axis of rotation of the brake shaft.
 19. The hydraulic drive apparatus of claim 18, wherein the center section further comprises a first check plug opening, a second check plug opening and a bore, and the first and second check plug openings and the bore form a triangular shape on one end of the center section.
 20. The hydraulic drive apparatus of claim 19, wherein the brake puck pocket is located adjacent to one of the first check plug opening or the second check plug opening. 